Light emitting diodes (LEDs) are becoming increasingly widely used in automobile design because of their longer lives and lower repair cost compared to the incandescent bulbs they replace. Present day automotive designers are specifying LEDs not only for indicator lamps and alphanumeric displays but also for high power illumination lamps such as center with mounted stop lights. LED stop lights require very high brightness, but only over a limited viewing angle.
In order to be cost competitive with incandescent bulbs, an LED stop light must contain only a minimum number of individual LED lamps. The number of individual lamps can only be minimized if each lamp extracts substantially all of the light flux from the LED chip and concentrates the light within the useful viewing angle. Light flux outside of the viewing angle is wasted and might have been available to increase brightness within the viewing angle.
Commercially available indicator lamps, which are designed according to the principles of imaging optics and standard manufacturing techniques, fail to concentrate sufficient light flux within the narrow required viewing angle. The imaging optics design constraint that the emitting surface is imaged by the viewing optics makes design of a cost effective LED illumination lamp using imaging optics very difficult.
An alternative design approach known as nonimaging optics has been used successfully in the design of high efficiency solar collectors. An additional degree of design freedom is available in nonimaging optics since there is no requirement that the emitting surface be imaged.
However, the design methods well known from the extensive literature on so-called ideal solar collectors or concentrators do not yield practical designs for high efficiency lamps. A practical collector design, when used as a lamp by replacing the absorber with the same size or larger emitter, as taught by the solar concentrator prior art, would result in trapping of a portion of the light flux from the emitter and thus lower lamp efficiency. The present design for the flux extractor cup for an LED lamp seeks higher efficiency not "ideality" in the solar collector sense.